1. Field of the Invention
This invention relates to aqueous solutions or suspensions containing glycidoxypropyl silanol and polydimethyl siloxanes having a number average molecular weight or more than 100,000 as mold release agents for plastics.
2. Statement of Related Art
Various mold release agents containing the following substances are known and are commercially available:
1. water-soluble surfactants; PA1 2. silicone oils containing organic solvents; PA1 3. crosslinkable silicone resins containing organic solvents, and PA1 4. silicone latices.
In addition to certain advantages however, the mold release agents disclosed above also show serious disadvantages. Thus, although they show ready biodegradability and produce a good release effect, the mold release agents of group 1 are stripped from the mold during each release cycle. To produce a thin film on the mold, the mold release agents of group 2 have to be dissolved in organic solvents. Since these solvents are inflammable and since the mold release agents are applied to molds heated to around 160.degree. C., they can only be used in explosion-proof plants. If, on the other hand, non-inflammable halogenated hydrocarbons are used as the solvents, the usual disposal measures have to be taken due to the solvent vapors formed. The mold release agents of group 2 also have to be re-applied after each cycle. In addition, they remain behind on the surfaces of the molding which therefore have to be cleaned before lacquering.
The mold release agents of group 3 have the disadvantages already mentioned due to the presence of solvents in them, although they do remain in place for several molding cycles. Although the mold release agents of group 4 are free from organic solvents, they are also easily stripped so that they often have to be re-applied and, in addition, cause soiling of the mold in practice. Accordingly, there is a need for mold release agents which are free from organic solvents and which do not have to be replaced for at least several molding cycles.